Buglyst Blog
Learn to debug under pressure.
Playbooks for fast pattern recognition, guides for the full investigation, and articles for the engineering judgment around the edges.
17 playbooks · 509 guides · 95 articles · 12 linked practice labs ·skip to practice
Fast pattern recognition for the production failures engineers see most often.
17 playbooks
Debugging Env Var Issues
A concise checklist for incidents where local works but CI, staging, or production changes behavior.
Debugging Cache Stampedes
How to recognize and contain request spikes when cached data expires.
Debugging CORS Origin Bugs
A practical way to inspect origin parsing, credentials, and header behavior.
Debugging Retry Bugs
Retry issues often hide the first failure and create duplicate work.
Debugging Timezone Bugs
Time bugs usually live at day boundaries, DST changes, and unit conversions.
Debugging Pagination Bugs
Pagination bugs hide in boundary math, cursor reuse, and new records arriving between pages.
Structured investigations for the failure modes engineers meet in real systems.
GraphQL Subscription WebSocket Not Receiving Events
A step-by-step debugging guide for when GraphQL subscriptions fail silently over WebSocket—no events, no errors, just silence.
Apollo Client Cache Not Updating After Mutation: How to Force a Normalized Cache Refresh
If Apollo Client returns stale data after a mutation, your normalized cache isn't merging correctly. Here's how to diagnose cache policies, field merge functions, and cache redirects.
Svelte Store Not Updating Component – Reactive Assignment Pitfalls
Learn how to debug a Svelte store that doesn't trigger component re-renders. Covers reactive assignments, store subscriptions, and common Svelte reactivity gotchas.
Debugging Apollo Federation Subgraph Errors: A Field Guide
A practical guide to diagnosing and resolving errors from Apollo Federation subgraphs, including type resolution failures, entity lookup issues, and gateway-subgraph communication problems.
Svelte Reactive Statement Not Re-running After State Change
A deep guide to debugging Svelte reactive statements that fail to re-run: covering dependency tracking pitfalls, stale closures, and assignment traps.
SvelteKit load function errors: root cause analysis and fix patterns
A practical guide to diagnosing and fixing errors in SvelteKit load functions, covering server vs client context, serialization issues, and timing pitfalls.
Long-form thinking on debugging habits, observability, and the systems around the bug.
How to Reproduce a Flaky Test: From CI Logs to Reliable Failure
A practical guide to turning intermittent test failures into reliably reproducible bugs, with techniques ranging from loop testing to thread sanitizers.
Property-Based Testing: Finding the Off-by-One That Lived in Production for 18 Months
A concrete story of how switching from example-based tests to property-based tests caught a timing bug that had survived code review, QA, and 18 months of production traffic.
How We Reduced End-to-End Test Flakiness by 80% with Deterministic Seeding
After months of chasing intermittent failures in our CI pipeline, we implemented a three-part strategy — deterministic seeding, isolated state per test, and a structured retry budget — that cut flaky end-to-end test failures by 80%.
Snapshot Testing: The 5 Hidden Failure Modes That Will Break Your CI
Snapshot tests seem like a safety net, but they often hide real bugs, bloat diffs, and silently break your CI. Here are the five failure modes I've seen in production and how to fix them.
Testing Async Code: Avoiding Flakiness and False Positives in JavaScript
Async testing is full of traps: unhandled rejections, race conditions, and tests that pass when they shouldn't. Here's how to write reliable async tests in JavaScript.
Testing Error Handling Code Paths: A Practical Approach
Error handling code is often the least tested and most brittle. Here's how to cover those paths with fault injection, mocks, and chaos engineering.